Sound reproduction system



Jan. 4, 1949. V w. J. ZENNER 2,458,043

. SOUND REPRODUCTION SYSTEM Filed Oct. 13, 1945 2 Sheets-Sheet l T0 SIGNAL SOURCE ATTORNEY Jan. 4, 1949. w. J. ZE 'NER 2,458,043

SOUND REPRODUCTION SYSTEM Filed Oct. 15, 1945 2 Sheets-Sheet 2 l NVENTOR WALTER J. ZENNER ATTORNEY Patented Jan. 4, 1949 UNITED STATES PATENT oFFi'ce Walter J. zennei'i Des Plaines, 111. Application October 13, 1945, Serial No. 622,178

7 Claims. (01. 179108) This invention relates to sound reproduction systems and more particularly to apparatus for converting electrical signals into sound waves.

The principal object of the invention is to provide a closed pneumatic system of sound reproduction having sound frequency air valves to modulate the air flow.

Another object of the invention is to provide a low frequency loud speaker of high power output which operates with a very small electrical signal input.

A feature of the invention resides in the method of utilizing the electrical signal input to control a flow of power from a local source to produce sound waves of greater power than the original electrical signal.

The foregoing and other objects and features of the invention are achieved by providing an enclosed air circulating system, wherein a blower driven by any convenient power means produces a flow of air through a chamber, one wall of which is capable of vibrating at sound frequencies. At the entrance to, and exit from this chamber, electrically operated air valves are provided which vary the air pressure within the chamber by modulating the air flow at the desired sound frequencies. As the air pressure within the chamber is varied, the movable wall of the cham-. ber is caused to vibrate, producing sound pressure waves in the adjacent external atmosphere.

A better understanding of the invention may be had from the following description taken in conjunction with the accompanying drawings,

wherein Y 1 Fig, 1 shows schematically a complete sound reproducing system utilizing the principles of the present invention;

Fig. 2 is a fragmental view taken on line 2--2' ofFig. 1.;

Fig. '3 is a fragmental sectional view of an alternate form of diaphragm;

.Fig. 4.is an enlarged sectional view of the air. valve shownin Fig. 1; 4

Fig. 5 is a sectional view taken on line 5-6 of,

. 45 Fig. 6 is a schematic fragmental view of a mod- Fig. 4;

ifled form of the invention, and

' Fig. '7 is a fragmental view of a further form of the invention.

Having reference to the drawings in which like characters represent similar parts throughout the several views, the sound reproducing unit accord ingto the present invention comprises a sound chamber I I consisting'of a movable. wall. I2 and a; fixed solidrear wall I3 joined by a flexible sealing strip I4. The wall I2 is riveted, or otherwise suitably secured, .to a plurality ofuresilientroi' yieldable brackets I5, preferably of U-shaped conformation, which are attached to the rear face of the wall I3 by means of screws 16. The sound chamber II encloses a quantity of air normally at atmospheric pressure. Under this condition of rest, the movable wall I2 occupies the position indicated in Fig. l. A small leakage port I! in the rear wall permits air to flow in or out of the chamber I I to establish an average pressure within the chamber II which is equal tothat of the external atmosphere.-

Air is introduced into the sound chamber II through a port or opening I8 which in the embodiment shown in Fig. 1 is flared toward the inside of chamber II and is provided with a deflector or baflle I9. The air stream flows through chamber II inthe direction indicated by the arrow and passes out through a port 2| similar to the opening I8. In registry with the openings I8 and 2| are the mouths of conduits 22 and 23, respectively. Conduit 23 is supportedby a casing secured to the solid rear wall I3 by -means of screws I6 and 25 and terminates in .a storage chamber 26. A conduit 21 is attached to the chamber 26 and is connected to theintake of a blower 28. The discharge end 29 of the blower 28 is attached to a'storage chamber 3I to which the conduit 22 is also attached. Conduit 22 is likewise supported by a casing 24..

Disposed between storage chambers 26 and 3I and secured thereto are a pair of bellows 32 and 33 which are separated by a wall 34 to which they-are also attached. The wall 34 is normally urged toward the chamber 3I by spring 35. Preferably, the wall 34 is provided with a flexible diaphragm 36 for filteringout pulsations of air pressure within the storage chambers 26 and 3|. The blower 28 drawsair from the negative chamber 26 and discharges itinto the positive pressure chamber 3|. The movable wall between the bellows 32 and 33 moves upward (as viewed in Fig. 1) as pressure develops, thereby tensioning the springs 35 to store energy. The diaphragm 36 will be normally distended by the average difference in the air pressures in the two chambers 26 and 3|. 7 ture, the diaphragm 36 will be free to vibrate,

permitting cancellation of those pulsations which are opposite in phase.

.Enolosedineach casingf24- and operatively-asisociated with the conduit 22 23); is. a control: ve a r m co ri n g y eiil Yam 31 ;(Figs. 1 aud t), the ,movement or which are Because of its flexible'naa controlled by moving coils 38 of local field magnets 40 of the electro-dynamic type commonly used in loud speakers. Each vane 31 is provided with side walls 39 connected by a web portion 4| through which the vane 31 is secured to its associated coil member by a screw 42. On each side of conduit 23 and preferably integral therewith, is a lug 43 to which the side walls 39 of vane 31 are hingedly fastened by means of flat spring hinges 44.

Each vane 31 is also provided with a shutter portion 45 of arcuate conformation determined by the radial distance from the hinge 44 and lug 43. The end of the conduit 23 adjacent the shutter portions 45 is of corresponding arcuate conformation, and the wall I3 is cut away adjacent the shutter portion to thereby provide a suitable pathway for said shutter.

The moving coil electro-magnets 38 each carry an operating winding, and these windings are connected in series over an obvious circuit or;- tlnding from an amplifier 46, over conductor 4?, through the several coils or operating windings toground. Local field magnet 40, previously mentioned, comprises a core 43, Winding 49 and return poles II, and may be of any suitable design. An extension pole 32 projects into juxtaposition with coil member 38, and is shaped to fit closely thereto. Field windings 49 are connected in an obvious circuit, such as diagrammatically shown in Fig. 1. extending from battery to ground over conductors 53 and 54, and in parallel through the field windings 49 of the several field magnets 45. The local field magnets 40 are adapted to be appropriately positioned angularly within the housing 24 by means or suitably designed supporting brackets 50.

The coils 3B or the air valve magnets are connected to conductor 41 so that both vanes 31 of the pair of vanes move outwardly or away from each other to increase the air flow, or inwardly (and toward each other) to reduce the air flow through conduits 21 or 23, as the signal current strength from amplifier 46 varies. The valve at the entrance I! is opposed in its action to the valve at the exit 2 I, so that one opens as the other closes and vice versa. A nincreaseinsignalcurrent strength therefore will cause both vanes 31 of the valve at the entrance 2| to move outwardly, increasing the air flow into the sound pressure chamber l I, and simultaneously the two vanes 31 of the valve at the exit II will move inwardly to reduce the air flow from the sound pressure chamber I i. This combined action increases the quantity and therefore the pressure or the air within the sound pressure chamber H, and drives the movable wall 02 from the solid line position (Fig. 1) outwardly to the dotted line position 55.

A reversal in the signal line current will reverse the' action the two valves associated with conduits 22 and 23, increasing the rate of flow from the chamber II and reducing the rate of now into the chamber. This action reduces the quantity of air and also the pressure with the chamber II and causes the movable wall l2 to move to position 56 (Fig. l). A continuously varying signal will cause the two air valves to oscillate and modulate the air pressure within the sound pressure chamber H in accordance with the wave form of the input signal. The ing pressure within the chamber I l is transmitted to the external atmosphere by virtue of the motion or the movable wall I 2.

The action of this pneumatic circuit is somewhat analogous to that or a simple vacuum tube amplifier circuit wherein a battery provides electrical pressure to drive an electrical current through a load impedance under the control oi a vacuum tube grid. The blower 23 and pressure chamber I l in the electro-pneumatic system compare with the plate battery, and the sound pressure chamber ll compares with the load impedance. The electro-pneumatic valves enclosed in housings 24 correspond to the vacuum tube grids. The push-pull arrangement of the valve elements also follows similar arrangements used in conventional electronic circuits.

In the specific embodiment shown in the Figs. 1, 4, and 5, the air passages or conduits 22 and 23 adjacent to the shutters 45 of vanes 31 are of cellular construction, thereby functioning as though a length of the passageway were built oi a large number of small tubes 57 grouped to form a single channel. As the shutters 45 move, the cover or uncover the ends of these tubular passageways 5! and block the flow of air throughout the full length of the individual tubes 5?. In this manner, the effective cross section controlled by the shutters 45 is greatly increased, and may be built to any desired length. By this means, it is possible to modulate the air fiou exactly in proportion to the current flow in the signal circuit should this be found to be desirable. As shown in Fig. 5. the confronting edges 58 and 59 of the shutters 45 are inclined with respect to the cellular openings 5'1 so tha, the air tubes or openings 51 are successively closed as the valve vanes 31 move inwardly and. outwardly.

Instead of a single entrance valve and a single exhaust valve, a plurality of valves H24 may be employed as shown in Fig. 6, to permit more rapid change of pressure within the sound pressure chamber i I. By this means a large chamber H may be used, and. yet a ver short distance maintained between the intake and exhaust valves. With such an arrangement, all intake valves will operate in unison, and all exhaust valves will operate in unison to produce the effect of the single valves shown in Fig. 1.

With the use of a plurality of air valves, as shown in Fig. 6, it is possible to arrange the return lines from the exhaust valves to the vacuum chamber 26, and the supply lines from the pressure chamber 3| to the intake valves so that each line is of different length. This is a desirable feature as it aids in filtering out the eii'ects of the pulsating air stream on the air pressure in the two chambers. It is desirable, of course, that the air pressure in the two storage chambers remains constant and that the modulating effects of the air valves not be allowed to appreciably change it. By providing valve supply and return lines of various lengths, the pulsations from individual valves will not reach the pressure chambers concurrently, but will be distributed over an appreciable period of time. If only one air valve were used, the full impact of the pressure reaction would be delivered to the pressure chamber in a single impulse requiring appreciably more air pulsation filtering than is required with the multi-valve design. In either case, however. it is expected that a certain amount of sound absorbing material will be required within the air storage chambers and associated supply lines connecting them with the blower, to prevent undesired repetitions of sound impulses.

In Fig. 3 is shown an alternative form of diaphragm or sound pressure chamber in which the diaphragm 8| is connected to the solid rear wall I! by means of a V-shaped flexible connection 62 reinforced or stiflened by rings 63.

In Fig. 7 is shown an embodiment of the invention embodying a two-directional loud speaker comprising a pair of diaphragms 'Il mounted on the solid wall I: by means of flexible connections 12 and reinforced by rings 13. In this form of the invention, the valve housings 24 are disposed around the periphery of wall l3 and ports 14 lead from the valve housings 24 into each air chamber 15.

Several embodiments of the invention have been shown and described. It will be understood that various modifications may be made in the constructions shown and particularly described within the purview of the invention as defined in the following claims.

What is claimed is:

1. In a pneumatic system of sound reproduction, an enclosed air circulating path including a chamber, said chamber having a wall adapted to vibrate at sound frequencies, a blower for producing a flow of air through said path, a first electrically operated air valve associated with said path adjacent the entrance to said chamber, a second electrically operated air valve associated with said path adjacent the exit from said chamber, electrical circuit means connecting said first and second electrically operated air valves, whereby in response to signal impulses said valves are alternately operated in opposition to produce a push-pull eifect upon the flow of air through said path.

2. In a sound reproducing system, a source of sound frequency signals, a closed pneumatic circuit including a sound chamber having a vibratabie diaphragm, air pressure control means in said circuit, air valves for controlling the air stream through said pneumatic circuit, and signal responsive means controlled by signals from said source for actuating said valves to modulate said air stream, certain of said signal responsive means adapted to operate in opposite to others of said signal responsive means to produce a push-pull eflect, whereby electrical signals are converted into sound waves through the instrumentality of said diaphragm.

3. In a sound reproducing system, a source of sound frequency signals, a closed pneumatic circuit including a loud speaker, air pressure control means in said circuit, and units controlled by electrical signals from said source for governing the flow of air through said pneumatic circuit, certain of said units adapted to operate alternately in opposition to other of said units to produce a push-pull effect, whereby said sound frequency signals are converted into sound waves.

4. In a sound reproducing system, a source of sound frequency signals, a closed pneumatic circuit including a pneumatic loud speaker and communicating tubes therefor, said tubes being of cellular construction, air pressure control means associated with said tubes, air valves cooperating with the cellular passageways of said tubes for controlling the air stream through said pneumatic circuit, and signal responsive means controlled by signals from said source for actuating said valves to modulate said air stream, whereby electrical signals are converted into sound waves.

5. In a sound producing system, a source of sound frequency signals, a closed pneumatic circuit including a pneumatic loud speaker and communicating tubes therefor, air pressure control means associated with said tubes, air valves cooperatin with said communicating tubes for controlling the air flow through said pneumatic circuit, and signal responsive means controlled by signals from said source for actuating said valves to modulate said air flow, certain of said signal responsive means adapted to operate in opposition to others of said signal responsive means to produce a push-pull effect, whereby electrical signals are converted into sound waves through the instrumentality of said loud speaker.

6. In a sound reproducing system, a source of electrical signals, a closed pneumatic circuit including a pneumatic loud speaker and communicating means therefor, said communicatin means being of cellular construction, a source of air pressure associated with said means, air valves cooperating with the cellular passageways of said communicatin means for controlling the air flow through said pneumatic circuit, and signal responsive means controlled by signals from said source-for actuating said valves to modulate said air flow, whereby said electrical signals are converted into sound waves.

'7. In a sound reproducing system, a source of electrical signals, a closed pneumatic circuit including a pneumatic loudspeaker and communicating means therefor, said communicating means being of cellular construction, a source of air pressure associated with said means, air valves cooperating with the cellular passageways of said communicating means for controlling the air flow through said pneumatic circuit, and signal responsive means controlled by signals from said source for actuating said valves to modulate said air flow, certain of said signal responsive means adapted to operate in opposition to others of said signal responsive means to produce a push-pull effect, whereby said electrical signals are converted into sound waves through the instrumentality of said loudspeaker.

WALTER. J. ZEN'NER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 592,769 Erdman Nov. 2, 1897 1,730,530 Robbins Oct. 8, 1929 1,829,991 Hetzel Nov. 3, 1931 2,179,815 Conklin Nov. 14, 1939 2,141,208 Eaves Dec. 2'1, 1938 2,204,808 McNeal June 18, 1940 

